Interviewing family members and friends is clearly a form of research, but interviews alone are usually not enough to give your stories the depth they require. For that, you need formal research.
Perhaps you already know enough about the period in which you or an ancestor ( a parent, grandparent) lived to write about it convincingly and fully. It is more likely, however, that you have only a sketchy knowledge of the context of your story.
Your awareness, for instance, may be based on a child’s limited perspective rather than the adult’s broader, more insightful one. You may know what your family had by way of household items but not whether those items were commonplace or whether they reveal your family’s special status (e.g., either more or less comfortable than most people).
In this video, You Need Formal Research, we look at ways to flesh out what you know about your background. Your memoir will be the better for it.
Be sure to like this post so that it becomes more available to other writers.